A bar code wand reads a bar code symbol over which it is drawn by illuminating the symbol with a beam of light and detecting the amount of illuminating light reflected from the symbol. A bar code symbol generally consists of an alternating series of reflective and nonreflective bars in a linear pattern. The variations in reflective and nonreflective bars determines the amount of reflected light that is detected. The detected illuminating light is converted into an electrical signal which is processed to determine the information contained in the symbol. The variations in the amount of light contain information in the form of variations in duration of the electrical signals which result when the bar code wand is drawn across the bar code symbol.
Handheld bar code scanners are powered by batteries. While the batteries are usually rechargeable, any loss of battery power by a handheld bar code scanner will quite possibly cause it to lose any data which it might have stored. Accordingly, it is important for a handheld bar code scanner to minimize its consumption of battery-supplied electrical power.
Most handheld bar code scanners are used intermittently, so that there are frequent long periods of time when the scanner is unused. While a handheld bar code scanner can generally be turned off to reduce electrical power consumption (without jeopardizing the data stored), it is desirable for the handheld bar code scanner to be immediately ready for use, without having to wait for the scanner to reset itself such as is required after the scanner is turned back on for use. Accordingly, it is further desirable to reduce consumption of electrical power.
One of the greatest power consuming elements in a handheld bar code scanner is the illumination beam source. The illumination beam is only needed when the scanner is sufficiently close to a surface which may carry a bar code symbol that it can be used. Accordingly, it would be useful to have a handheld bar code scanner which enters a quiescent mode when it is not near a surface, which might bear a bar code symbol, but which activates to read the bar code symbol when it is brought close to a surface which may bear bar code symbols.